Using the RS3ExTool2 Tool
RS3ExTool2 is a tool for RS3 which can import and export music formatted as Music Macro Language files. It can also export music from several SNES games, though for some reason it's only worked with headered roms for me.
The bottom right button is the import button, the bottom left the export button. The checkboxes are for determining where in RS3 the song will play. The left box under the MML selection is the song index, the right box is the offset where the song will go.
You can set up the instrument index for the song with this:
#WAVE 0x20, 0x12; #WAVE 0x21, 0x29; #WAVE 0x22, 0x3C; #WAVE 0x23, 0x10; #WAVE 0x24, 0x0E; #WAVE 0x25, 0x0A; #WAVE 0x26, 0x00; #WAVE 0x27, 0x00; #WAVE 0x28, 0x00; #WAVE 0x29, 0x00; #WAVE 0x2A, 0x00; #WAVE 0x2B, 0x00; #WAVE 0x2C, 0x00; #WAVE 0x2D, 0x00; #WAVE 0x2E, 0x00; #WAVE 0x2F, 0x00;
Some of the commands added to correspond to "S-SPC" commands:
@<n> - SetInstrument (Command DC) (ex. @0x20) %k<n> - Tranpose (D9) %b<n> - SetEchoFB (F7) %f<n> - SetFirCoeff (F8) p<n> - ChanPan (C6) %e1 - EchoOn (D4) %e0 - EchoOff (D5) %v<n> - Echo volume t<n> - Tempo v<n> - volume o<n>- Octave
If you're converting a MIDI to a MML, it likely won't have the commands needed, except maybe octave. You'll have to insert them into the channels. Parameters are generally in decimal.